1. Field of the Invention
The present invention is concerned with eyewear having electronically controlled lens structures in which the optical transmissivity thereof is automatically adjusted to a level correlated with the level of ambient light. More particularly, the present invention is concerned with eyewear in which a control circuit senses ambient light level and adjusts the transmissivity of the eyewear lens structures to a level correlated with the ambient light level.
2. Description of the Prior Art
Eyewear is known in the prior art which uses so-called PHOTOGRAY lens. These lens include a light-sensitive chemical structure which chemically darkens upon exposure to ambient light. The PHOTO-GRAY lens present a problem, however, in that with age, the sensitivity decreases thereby taking longer to respond to changes in ambient light levels. Additionally, the PHOTOGRAY lenses have a fixed sensitivity to ambient light, that is, have a fixed correlation with the level of ambient light.
The prior art also discloses electronically controlled lenses such as disclosed in U.S. Pat. Nos. 3,519,339, 3,245,315, and 4,039,803, the disclosures of which are hereby incorporated by reference. These prior art devices, such as that disclosed in the '315 patent, are designed to prevent eye damage from suddenly occurring high levels of ambient light in order to prevent flash blindness, for example. With this objective, these prior art devices devices are designed to automatically and quickly shift from a relatively transmissive condition to a relatively opaque condition upon the occurence of a high level of ambient light. These devices are not suitable, however, for use as day-to-day eyewear because they cannot produce varying levels of transmissivity correlated with varying levels of ambient light. Additionally, the prior art devices are powered solely by a battery pack which must be frequently replaced if the eyewear is frequently used.